Medical professionals and cytotechnologists frequently review biological specimens affixed to a specimen carrier, such as a slide, to analyze whether a person from whom the specimen was obtained has or may have a particular medical condition. For example, it is well known to examine a cytological specimen in order to detect the presence of malignant or pre-malignant cells as part of a Papanicolaou (Pap) smear test. To facilitate this review process, automated systems have been employed to perform a pre-screening of the specimen slides in order to focus the cytotechnologist's attention on the most (or at least more) pertinent cells or groups of cells in the respective specimen, while discarding less relevant cells from further review. One such automated imaging system is the Thinprep Imaging System, available from Cytyc Corporation, 250 Campus Drive, Marlborough, Mass. 01752 (www.cytyc.com).
More particularly, referring to FIG. 1, a cytological specimen 10 is prepared and carried by a slide 12. The cytological specimen 10 includes a number of portions 20, e.g., a first portion 21, a second portion 22, a third portion 23, etc. FIG. 1 generally illustrates square-shaped portions for purposes of illustration. The number of portions 20 can vary depending on the size of portions 20, the size of the specimen 10, and the size of the area of the specimen to be imaged. For example, a specimen 10 can include about 3,000 portions 20 that are to be imaged.
Referring to FIG. 2, each portion 20 may include various cytological components, including cells 30. Each cell 30 includes a nucleus 32 and cytoplasm 34 surrounding the nucleus 32. The area of a portion 20 that is not occupied by cells 30 is generally referred to as background 36. The collection of portions that forms a specimen includes a collection of cells 30 and background 36 areas.
Referring to FIG. 3, a specimen slide 12 is processed by an imaging system 40, such as the Thin Prep Imaging System. One exemplary imaging system 40 is also described in U.S. Pat. No. 7,006,674, the contents of which are incorporated herein by reference as though set forth in full. An imaging system 40 typically includes a stage 42 upon which the slide 12 is placed, a camera 44 for taking images of the specimen 10, and a processor or controller 46 for controlling the stage 42 and the camera 46. The imaging system 40 can also include other components, as described in the above-incorporated U.S. Pat. No. 7,006,674.
In use, the camera 44 acquires an image of a first portion 21 of the specimen 10. The stage 42 is moved to move the specimen 10 so that the next portion 22 is in view of the camera 44. An image of the second or next portion 22 is acquired by the camera 44. The stage 42 is moved, and so on, until an image of each necessary portion 20 is acquired. In known systems, the image of each portion 20 is acquired at a particular brightness or exposure level that is selected to be sufficiently bright so that most sections of the image (cytoplasm 34 and background 36) are sufficiently bright and visible.
For example, referring to FIG. 4, in one known imaging system, the camera 44 is set to an exposure level of 229 based on a 0-255 grayscale. The result of this exposure setting is that the image of a portion 20 of the cytological specimen 10 has background 36 at a brightness level of 229, cytoplasm 34 at a brightness level about 50 to 150, e.g., about 100 to 150, and nuclei 32 at a brightness level of about 20. While this exposure setting may be suitable for cytoplasm 34 and background 36, nuclei 32 in the image are not very visible since the brightness level is only 20.
While known systems and methods have been used effectively to image cells in the past, they can be improved. Initially, the resulting brightness of different cytological components can vary significantly, and with known imaging systems, it is not always possible to see individual cell nuclei 32 and nuclei 32 that are clumped together. For example, as shown in FIG. 4, the brightness of the nuclei 32 in the image is only about 20. Thus, the shape, size, color, and internal components of nuclei 32 may not be observable. These shortcomings may be more pronounced when attempting to view cell nuclei 32 that are clumped together. Further, smaller nuclei 32 details may not be observable at all at these low brightness levels.
One potential solution to this problem is increasing the brightness or exposure so that the nuclei are brighter. However, this is not very feasible. If the exposure setting is 229, the exposure can only be increased to 255 (i.e., about a 10% increase in exposure). This results in increasing the brightness of nuclei 32 by about 10%, i.e., increasing brightness from 20 to about 22. This nominal increase in brightness is not sufficient to provide the desired image quality and nuclei 32 detail. Additionally, the camera cannot resolve anything brighter than 255, and details in the brighter background and cytoplasm sections are lost as the pixel values peak at a brightness of 255. Thus, increasing the increasing the exposure only provides minimal improvement to nuclei 32 brightness while degrading other portions of the image.
It would be advantageous, therefore, to form an optimally exposed image of a cytological specimen. It would also be advantageous to form an image with brighter nuclei and groups of nuclei without saturating other parts of the image. It would also be desirable to illuminate nuclei and portions thereof that were not previously visible using known systems.